Material deposition is widely used in window glass coating, flat panel display manufacturing, coating on flexible films (such as webs), hard disk coating, industrial surface coating, semiconductor wafer processing, photovoltaic panels, and other applications. Target materials are sputtered or vaporized from a source and deposited on a substrate. One desirable feature for material deposition is to maximize the utilization and to minimize waste of target materials. Another desirable feature for material deposition is to achieve uniform deposition across the substrates.
Different designs exist in the conventional deposition systems for large substrates. But the designs all have different drawbacks. In a first example, referring to FIGS. 1A-1D, a deposition system 100 includes a long narrow rectangular target 110 over a large substrate 115 in a vacuum chamber 120. A magnetron 130 is held behind the target 110. The substrate 115 can be transported in the direction 150 relative to the target 110 and the magnetron 130 to receive a uniform deposition across the top surface of the substrate 115. The magnetron 130 is stationary relative to the target 110. The deposition system 100 can also includes a power supply 140 that can produce an electric bias between the target and walls of the vacuum chamber 120.
The magnetron 130 includes a magnetic pole 132 of a first polarity and a magnetic pole 135 of a second polarity opposite to the first polarity. The magnetron 130 can produce magnetic flux outside of the sputtering surface 112 on the lower side of the target 110 as shown in FIG. 1B. More electrons can be confined near the magnetic field parallel to the sputtering surface 112 wherein the magnetic field strength is at local maximum. The locations having the locally maximum magnetic field strength can form a close loop that can guide the migration path for free electrons. The closed-loop magnetic field can enhance the ionization efficiency of the sputtering gas (i.e. the plasma) for more effective confining electrons near the sputtering surface 112. The enhanced ionization can also lower the operating pressure during sputter deposition.
A drawback of the deposition system 100 is that a non-uniform erosion pattern 115 is often formed over the sputtering surface 112 of the target 110 after repeated sputtering operations. The erosion pattern 115 usually tracks the location where the magnetic field strength is at local maximum and where the sputtering gas is the most enhanced. The erosion pattern 115 include a close-looped groove as shown in FIG. 1D. The non-uniform erosion can result in low target utilization and re-deposition of sputtered target materials on the areas of the sputtering surface 112 having low magnetic field strength. Some of the accumulated materials can fall off the target 110 and cause undesirable particles to be deposited on the substrate 115. Another disadvantage of the deposition system 100 is that the larger dimension of target needs to be wider than the width of the substrate to achieve good deposition uniformity; some sputtered material will unavoidably not reach the substrate surface and thus be wasted. Referring to FIGS. 2A and 2B, another conventional deposition system 200 includes a large target 210 having a sputtering surface 212, a vacuum chamber 220, and a magnetron 230 on the back side (opposite to the sputtering surface 212) of the large target 210. The magnetron 230 can scan across along the direction 250. The substrate 215 is held over a substrate holder 217. The substrate 215 can remain stationary during the deposition if a target has dimensions larger than the substrate 215. The scanning of the magnetron 230 relative to target 210 can cause target materials to be sputtered off different portions of the target surface to deposition on the deposition surface 217 along directions 260. To achieve uniform deposition, the target 210 is typically larger than the deposition surface on the substrate.
The disadvantages of the deposition system 200 include the requirement of a large and expensive target, as described above. Another disadvantage is the difficulty to achieve uniform deposition. Only the outermost part of the closed loop erosion track of the magnetron 230 can reach edge of the target 210, which tends to lower the sputtering at the edges of the target 210 and to cause non-uniform deposition over the substrate 215. Typically the target is significantly larger than substrate to achieve good deposition uniformity. More material and electrical power is used to deposit films on substrate due to extra deposition outside the substrate area. Another disadvantage of the deposition system 200 is that certain amount of the sputtered materials may be wasted. For example, the material sputtered in directions 260a and 260b cannot arrive at the deposition surface 217.